1. Field of the Inventions
This invention relates to apparatus suitable for annealing the interior walls of a nuclear reactor, particularly the vertical walls thereof, including the weld material in said walls, wherein said nuclear reactor is provided with a cap securely attached at the top thereof, said cap having a high-energy gas inlet extending inwardly therein and a low-energy gas outlet extending outwardly therefrom, means defining an annular space adjacent to the vertical walls of said reactor through which gas can flow and means for directing low energy gas to said low-energy gas outlet.
2. Description of the Prior Art
During the normal operation of a nuclear reactor, fast neutrons emanating from the core of the reactor create irradiation damage in the walls of the reactor, as well as in the weld material, resulting in the embrittlement of the metal, thereby reducing the metal toughness thereof. It is known that some, or all of the irradiated metal, can be restored to its initial, preoperational state by subjecting the same to elevated temperatures, for example, 423.degree. F. to 650.degree. F., for about 168 hours. It is known that a "wet" annealing process has been carried out on Belgian nuclear reactors with hot water at a relatively low temperature of about 262.degree. to about 650.degree. F. In Feasibility of and Methodology for Thermal Annealing an Embrittled Reactor Vessel (EPRI NP-2712, Volume 2, Project 1021-1, Final Report, November 1982, pages S-5 and S-6) it is stated that wet annealing at the relatively low temperatures will result in relatively low recovery of the reactor, but that "dry" thermal annealing, that is, without liquid in the reactor, using spent fuel assemblies, induction heating elements or resistance heating elements at temperatures on the order or about 850.degree. F. for about 168 hours, recovery of the embrittled walls is on the order of about 80 to about 100 percent. Means for carrying out a dry annealing process of the type described is illustrated in Report on Annealing of the Novovoranezh Unit Reactor Vessel in the USSR prepared by N. M. Cole and T. Fridericks for the U. S. Nuclear Regulatory Commission. On page 15, it is stated that for such purpose, there was used annealing L apparatus having a weight of 28.7 tons and carrying 54 heating panels distributed on the periphery thereof.
Using hot water in a nuclear reactor to reach an effective annealing temperature of about 850.degree. F. is virtually impossible, since the pressure required in the water at such high temperature would be so high as to seriously impair the structural integrity of the reactor walls. Normally, the water temperatures in a nuclear reactor cannot be raised above about 645.degree. F. Although it is possible to reach an effective annealing temperature of about 850.degree. F. using heating elements, as illustrated above in the Russian reactor system, all of the reactor, including the thermal shields therein, have first to be removed, the heating assembly is extremely large and expensive and it would be difficult to heat the reactor walls uniformly throughout, because it is likely that some portions of the wall heated by adjacent heating elements would have zones there-between that would not receive as much heat energy as the main heated portions, resulting in nonuniform heating of the walls.
Using the novel apparatus disclosed and claimed herein requires only simple alterations in the reactor to be treated, is simple to operate and will result in reactor walls that have been substantially completely heated to at any desired temperature level, for example, during the preheating stage as well as during the annealing stage.